The present invention relates to a formation fluid sampling and hydraulic testing tool for a drilling apparatus that includes a drilling string comprised of a drilling pipe and a drilling bit. The present invention further relates to a method of drilling and sampling with such a drilling apparatus.
Formerly, to obtain a valid formation fluid sample from single or multiple rock units within the earth, it was necessary to drill a borehole to the total depth, to run down-the-hole geophysical logs, to set casing cemented to the surface, to run a wireline shot-tool into the cased hole to a desired sampling location, to shoot holes through the casing and the cement-filled annular space behind the casing and into the formation, such that formation fluid can enter the interior of the casing, to set a straddle-packer across the shot zone, to insert a pumping device and pump the fluid out until its pH and electrical conductivity stabilize. The procedure of shooting the casing and setting a packer is repeated for as many formations as desired. If hydraulic testing is desired, a pressure transducer must be set between the upper and lower packers of the straddle packer and an electrical line must be run to the surface. These processes are costly and time consuming.
The former method has the further disadvantage that cracking of the cement in the annular space between the boreface and the steel casing can form a pathway for flow of formation fluids behind the casing resulting in possible cross-contamination and alteration of formation fluid pressures.
Alternatively side wall sampling devices try to extract fluid samples from a formation behind the mud cake on the boreface. Such samples are usually contaminated by drilling fluid, and the criterion of pumping until constant pH and electrical conductivity are achieved cannot be obtained.
One effort for improving the aforementioned procedures was described in U.S. Pat. No. 5,054,533. However, this effort does not provide the desired time and cost savings.
It is therefore an object of the present invention to provide a formation fluid sampling and hydraulic testing tool that significantly reduces the time and cost involved in the acquisition of samples of fluids contained within subsurface rock strata without removing the drilling tools from a borehole. Such a tool should also allow the determination of hydraulic characteristics of these same subsurface rock strata, again without removing the drilling tools from the borehole, and should prevent possible cross contamination and/or alteration of fluid pressures and provide better information for design of any well completions.